Optical Position Measuring Device with High-Efficiency Reference Gratings
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Solution Overview
Problem
Existing optical position measuring devices experience significant signal drops when scanning over reference marks, necessitating increased light source power which reduces the control reserve for compensating other issues like aging and soiling.
Innovation Solution
The device integrates reference marks with periodic and aperiodic sub-areas, arranged in specific configurations, to maintain signal levels without increasing light source power, using reflection phase gratings with enhanced scanning efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical power of the light source is increased when passing over reference marks, then the signal drop is avoided, but the control reserve for compensating aging and soiling is reduced
Solution Approach 1:
The patent applies local quality by creating reference marks with periodic sub-areas that have enhanced scanning efficiency specifically at reference positions, while the rest of the measuring scale maintains its original properties. This localized enhancement ensures sufficient signal levels at reference marks without requiring increased light source power across the entire measurement range, thereby preserving the control reserve for compensating aging and soiling effects.
Solution Approach 2:
The patent changes the structural parameters of the reference marks by introducing periodic sub-areas with specific grid patterns that have higher scanning efficiency. This parameter change in the reference mark structure allows for maintained signal levels without increasing the optical power parameter of the light source, thus avoiding the trade-off between signal level and control reserve.
2Adaptability or versatility
If reference marks are integrated into the measuring scale, then reference signal generation is enabled, but signal levels drop when scanning over reference marks
Solution Approach 1:
The reference marks are designed with periodic sub-areas that have locally enhanced scanning efficiency. This local quality enhancement ensures that while reference marks are integrated into the measuring scale for reference signal generation, the signal level drop is compensated by the higher scanning efficiency in the periodic sub-areas, maintaining overall measurement precision.
3Measurement precision
If the light source current is used to increase optical power, then signal drop is prevented, but the ability to compensate for aging and soiling is reduced
Solution Approach 1:
By enhancing the scanning efficiency locally in the periodic sub-areas of reference marks, the patent maintains signal levels without requiring increased light source current. This preserves the full dynamic range and control reserve of the light source for compensating aging and soiling effects over time, extending the effective duration of accurate operation.
Solution Approach 2:
The patent uses structural modifications in the reference marks (periodic sub-areas) as a 'disposable' or fixed feature that absorbs the signal level challenge, allowing the light source to operate at constant power with full control reserve available for long-term compensation of aging and soiling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures minimal signal drop during reference mark traversal, maintaining full control reserve for compensating aging and soiling effects.
Implementation Method 1
at least the periodic sub-areas of the reference marks exhibit a higher scanning efficiency than the surrounding measurement division
Implementation Method 2
using reflection phase gratings with enhanced scanning efficiency
Implementation Method 3
each having at least one light source
Implementation Method 4
each having at least one light source, one or more gratings, and a detector arrangement
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The present invention relates to an optical position measuring device for determining the relative position of two objects that are movable relative to each other along at least two measuring directions. For this purpose, several scanning units are provided, each connected to one of the two objects and comprising at least one light source, one or more gratings, and a detector arrangement. Furthermore, a scale is provided, which is connected to the other object. This scale has a two-dimensional measuring division consisting of structural elements with different optical properties arranged periodically along the two measuring directions. Several reference marks with periodic and aperiodic sub-areas are integrated into the measuring division. A reference signal can be generated from the scanning of the reference marks at a defined reference position along one measuring direction.At least the periodic sub-areas of the reference marks exhibit a higher scanning efficiency than the surrounding measuring scale (Fig.2).